The postcodes of the respondents were then compared to a socio-economic classification system developed by Experian.

This enabled the researchers to show which types of people tend to have high and low BMIs.

As the make-up of each town according to these categories is known, they were able to rank towns on their density of the number of people likely to have a high or low BMI.

The researchers claim their form of detailed geographical analysis could help local health service planners and clinicians target resources where they were most needed.

LOWEST RISK

City of London

Kensington and Chelsea

Westminster

Camden

Hammersmith and Fulham

Wandsworth

Richmond upon Thames

Islington

Barnet

Lambeth

Emily Sparks, a health consultant at Experian, said: "Through better health mapping, we can now provide timely and relevant information to enable the more effective targeting of communications and the delivery of preventative care to social groups and neighbourhoods most at risk of obesity."

However, Dr Ian Campbell, medical director of the charity Weight Concern, said obesity was a widespread problem - and doubted the merits of a highly targeted approach.

He said: "The management, prevention and treatment of obesity does not need fine tuning.

"The differences are small between regions, and we need a broad brush approach."